Embodiments of the invention relate generally to resonant sensors and, in particular, to resonant sensors that may be interrogated via the use of a combination of RF pulses and a magnetic field gradient being applied thereto, such that a resonant sensor will emit a unique phase and frequency pair based on it's positioning within the magnetic field.
Resonant sensors are sensors whose output can vary with respect to changes in specific environmental or biological conditions present near the resonant sensor. Typically, resonant sensors are comprised of an inductance-capacitance (LC) circuit with a specific resonance frequency. The resonant sensor is excited by an RF pulse and then its value can be read back by the amount of energy they emit as the LC circuit's resonant energy decays. In use, the amount of energy imparted into the resonant circuit can be proportional to the measurand (i.e., the object/substance being measured) and/or the frequency of resonance in the resonant circuit can be altered by the measurand. A readout of a resonant sensor can then be performed via a receiver that records the energy emitted from the sensor.
While use of a single resonant sensor raises no issues with regard to interrogation of the sensor and readout of the sensor via an associated receiver, it is recognized that issues arise when a sensor array composed of a large number of resonant sensors (e.g., 1000+ sensors) in close proximity to one another are to be interrogated and read out. That is, it is challenging to differentiate the response from each resonant sensor from the other proximate sensors such that the readout information from each respective sensor can be separated.
Several techniques have been employed in order to solve the problem of uniquely identifying sensors in a large sensor array. One common solution is for each sensor in the sensor array to be specifically designed to respond to a unique frequency or respond to a unique wave form (coding). However, this makes every sensor unique and leads to increased cost in manufacturing and providing the sensors for the sensor array. Another common solution is for each sensor to include complex electronics to harvest power from the RF interrogation signal, perform signal processing, and transmit a unique signal from the sensor. However, due to the amount of energy required for such electronics, a large antenna or coil is needed in the sensor that increases the size of the sensor. Additionally, the complex electronics in the sensor increases the cost in manufacturing and providing the sensors for the sensor array.
Therefore, it is desirable to provide a resonant sensor that is configured so as to enable the sensor to be uniquely identified and differentiated from other resonant sensors in a sensor array. It is further desirable that such a resonant sensor would have a common construction with other resonant sensors in a sensor array and not require complex signal processing electronics therein, such that the cost and complexity of the resonant sensor is minimized.